Serrated rotary knife paper trimmers for streams of paper products are known in the art. My U.S. Pat. No. 3,813,981 issued June 4, 1974 for Paper Trimming Knife System has an annular disc cutting knife with peripheral teeth overlapping in an arc and registered against a planar cutting surface of a rotary bed knife. U.S. Pat. No. 4,480,518 was issued Nov. 6, 1984 to K. Futterer for Apparatus for Trimming the Marginal Portions of Paper Sheets or the like. Therein radially disposed cutting knives are disposed for rotary contact with stationary counterknives to sequentially present a succession of shearing blades through the thickness of the product before engaging a surface of the counterknife.
In the prior paper trimming art there are several significant unsolved problems, generally resulting in high power drive requirements, short cutting blade life and ragged cutting edges. The problems are exaggerated when the thickness of the paper products is great as in the case of magazines for example, and when the products are shingled so that the cutting loads are not constant but vary over a succession of step function increases in loading. Heretofore, there has been no satisfactory solution to these blade life, loading and quality of cut problems presented with thicker shingled paper products at high conveyance speeds.
It is therefore an objective of this invention to solve these prior art problems and to provide a rotary paper trimming system that produces unexpected increases of knife life and quality of cut.
A further object of the invention is to provide improved methods of trimming thick shingled streams of fast moving paper products.
A still further object of the invention is to reduce power requirements, heat and friction in the trimming of paper products, and to significantly increase the lifetime of the cutting blades in standard or heavy duty applications.